So sorry! That is a total nightmare and makes my stomach sick even thinking about it! We have been really lucky with our
Brinsea, then, cause it was just a teensy bit low (.5 degree) but otherwise good. It is a Octagon Advance and we have the humidity pump so we don't have to worry about humidity--that part has been super nice. We also have a couple of the new hovabators, the new Genesis with built in hygrometer as well as temp. One of them was pretty accurate in both temp and humidity, the other was off on both but especially humidity. We keep a backup hygrometer in that one.
The thermometers we have NOT been happy with would make for a very long list, but unfortunately I don't remember names anymore as it's been a couple years. What we use now are the
Brinsea digitial thermometer (that's the one they replaced even though it wasn't off by much) which is a probe style and can be dropped down to the level of the eggs. That one came highly recommended and has been very nice. We also use a couple of other probe style thermometer that are intended for use in fish tanks, but they are only so-so. And lastly we take quick readings off the eggs themselves using an ear thermometer. Those range from $15-25 around here and I would go with a nicer end one. We were given the tip to use those by a guy at our State Vet Univesity who pointed out that the eggs can get quite a bit warmer due to their own developing metabolic heat just before hatch, and sometimes in large hatches can overheat unless the incubator is adjusted. To be honest, we haven't seen a big difference in the egg temperature there at the end, but we are doing smaller hatches or divided hatches. At any rate, if you decide to get the ear thermometer aim it at the bottom 2/3ds of the egg, so below the air sack, and you will probably only be able to do one or two eggs at a time and close the incubator in between so you're not affecting egg temp.
Lastly, the hygrometer we use is a Fluker (I think that's how it's spelled) which is the only hygrometer we've ever liked. It's intended for reptile use and sold in the reptile section of big pet stores. It's pretty accurate and we've used it to back everything else up.
Good luck! If you're bator isn't helping you I think that first while trying to get the setup working as it should can be pretty agonizing. Hang in there, and I hope this helps!